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## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Silicon Sea, LEG 13
From: Greg Rudzinski
Date: 2012 Sep 27, 19:29 -0700

Alberto,

The first give away that something is wrong is the time of twilight. December 5th at 36 north will have civil twilight at 1714. Now lets transpose the 5 & 12 and we get May 12 th with a civil twilight of 1926 which is a good fit for this exercise. The attached plot works out pretty good for 12 May 1996. The navigator could have done a better job of star selection though.

Greg Rudzinski

[NavList] Re: Silicon Sea, LEG 13
From: Alberto Najar
Date: 27 Sep 2012 21:47
Hi Greg,

Sorry, here we go: my problem was with the question 1. I think there is some thing wrong with the data. The text is:

"Sight Reduction and DR
---------------------- ------ ----------------------------

On 12/05/96 we are at DR(36d 13.9'N 10d 54.4'E), on a TC of 111.3d at
7.8 Kts bound for Masabb Dumyat(31d 30.1.N 31d 50.0'E).

It is 19-42-00 ZT. We decide on a set of 3 bodies for a FIX During
Evening Nautical Twilight.

Body Time Hs Zn

Sirius 19-42-56 11d 46.2' 239.1d
Alioth 19-48-27 61d 55.8' 035.8d
Spica 19-54-40 31d 59.7' 137.5d

1) What is our FIX position using Spica as the plotting time?
What is the Dist Off?"

If we work these sights we will find some thing very bizarre. I found:

LOP for Sirius
12/05/1996 19:42:56 GMT
Assumed Pos. Lat:36°13.9'N Lon:10°54.4'E

Hs: 11°46.2'
Dip:-2.7' IC:-0.2'
Ha: 11°43.3'
Ho: 11°38.7'

GHA: 65°20.5'
Decl: 16°43.0'S
LHA: 76°14.9'

Hc: 0°46.9'
Intercept:651.8 NM (towards)
Az.calc: 248°

LOP for Alioth
12/05/1996 19:48:21 GMT
Assumed Pos. Lat:36°13.9'N Lon:10°54.4'E

Hs: 61°55.8'
Dip:-2.7' IC:-0.2'
Ha: 61°52.9'
Ho: 61°52.3'

GHA: 334°28.3'
Decl: 55°59.0'N
LHA: 345°22.7'

Hc: 67°54.3'
Intercept:-361.9 NM (away)
Az.calc: 22°

LOP for Spica
12/05/1996 19:54:40 GMT
Assumed Pos. Lat:36°13.9'N Lon:10°54.4'E

Hs: 31°59.7'
Dip:-2.7' IC:-0.2'
Ha: 31°56.8'
Ho: 31°55.2'

GHA: 328°16.3'
Decl: 11°08.6'S
LHA: 339°10.7'

Calculated Altitude (Hc): 38°43.1'
Intercept:-407.9 NM (away)
Az.calc: 153°

Thank you very much,

Alberto.

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